The present invention relates to the removal of sulphur from sulphur-containing hydrocarbon feedstocks. The invention provides a novel metal sulphide catalyst, a process for preparing the catalyst, and a process for using the catalyst to remove at least a portion of the sulphur contained in such feedstocks.
Present day commercial hydrocarbon upgrading installations utilize hydrotreating to remove sulphur from the hydrocarbon feedstock. The feedstock is passed over a conventional hydrodesulphurization catalyst in the presence of hydrogen to remove sulphur in the form of hydrogen sulphide. Often the hydrodesulphurization catalyst comprises one or more transition metal sulphides, for example a sulphide mixture of cobalt molybdate.
While these hydrodesulphurization catalysts are successful in desulphurizing the feedstock, they require large amounts of expensive external hydrogen. Furthermore, the processes are practised late in the overall upgrading process, and thus all equipment upstream of the hydrotreating step must be manufactured from corrosive resistant materials to withstand the sulphur content.
Heavy hydrocarbons derived from such fossil fuels as oil sand bitumen and heavy oil typically contain very high amounts of sulphur. In particular, oil sand bitumen, large deposits of which exist in the Athabasca oil sand deposits of Alberta, Canada, contain about 4.5 to 5.0% by weight sulphur. A portion of this sulphur seems to be quite labile and is therefore slowly released throughout the upgrading processes. The sulphur is dispersed over various product fractions in the upgrading process and thus each of these fractions must be treated in expensive corrosive resistant equipment and ultimately be hydrotreated to remove the sulphur.
Thus any process capable of reducing the sulphur content of these sulphur-containing heavy hydrocarbons would be advantageous. A desulphurization process not requiring external hydrogen would be particularly advantageous.
Asphaltene is a solid component of fossil fuels generally defined as that solubility class which is precipitated from solutions of petroleums and bitumens in an aromatic solvent by the addition of a minimum of 40 volumes of n-pentane. Asphaltenes so derived can be pyrolyzed to recover useful volatile hydrocarbons. Hydrogen sulphide is also produced during the pyrolysis. The hydrogen sulphide can be removed from the pyrolysis product stream by conventional scrubbing techniques. A process which would increase the release of hydrogen sulphide during pyrolysis would be advantageous as the hydrogen sulphide can be easily removed and the amount of sulphur entrained in other forms in the pyrolysis products is reduced.
In U.S. Pat. No. 1,976,806 issued Sept. 18, 1931, to R. Rosen, a process is provided for desulphurizing normally gaseous petroleum products. The gaseous stream is passed over a catalyst comprising ferrous sulphide mixed with promoters consisting of oxides and sulphides of Group III and Group IV metals. The process is performed in the absence of hydrogen, but has only been shown to be effective with normally gaseous petroleum products.
Metal sulphide catalysts have been developed for purposes other than desulphurizing hydrocarbon sources. Exemplary are the catalysts disclosed in U.S. Pat. No. 2,559,325 issued to P. Spillane and U.S. Pat. No. 3,974,096 issued to M. Segura et al. These catalysts however are dissimilar to the catalyst of the present invention and are used in non-analogous processes.